(1) Field of the Invention
The present invention relates to acoustics and to apparatus for acoustically isolating a high-pressure steam line located within a flooded structure. More particularly, the present invention relates to such apparatus through which acoustic energy generated in the steam pipe assembly is prevented from radiating out into the surrounding fluid.
(2) Brief Description of the Prior Art
The acoustic isolation of high-pressure steam lines used to test equipment for torpedo drive train system presents certain unique challenges. That is, the acoustic measurement of noise caused by torpedo drive train systems is sometimes measured in a large fluid filled structure in which the torpedo is mounted. In one possible application, high-pressure steam can be used to power the vehicle for subsequent noise testing. This steam is transported to the vehicle via a piping system which runs from the steam generation source through the structure's wall and then through the fluid filled interior of the structure to the vehicle.
The prior art discloses various means for insulating pipes and tubing against the transmission of sound, heat or other forms of energy.
U.S. Pat. No. 3,595,275 to Stearns et al., for example, discloses a spacer for semiflexible coaxial tubing which comprises a strip of fibrous thermal insulating material having an abrasive resistant facing helically wound with opposite pitch around an inner tube. The spacer may include a moisture impermeable package, enclosing particles which functions as one or both of the facings after rupture to expose the particles. The spacer is used in coaxial tubing having evacuated annular spaces that provide an annular concentric space for flow of fluid between said evacuated spaces. Stearns et al. do not teach acoustic shielding or provide for high temperature fluids in the tubing.
U.S. Pat. No. 4,436,119 to Shahan et al. discloses a system for insulating and isolating a pipe, thermally and acoustically, from its outer metallic cover. The system consisting of a pipe jacket providing an external cover, an inner body of insulation such as fiberglass or the like, a vibration absorption unit and a series of spacers yieldably separating the jacket from the pipe to be insulated. However, the invention taught by Shahan et al. is inapplicable to underwater environments because the acoustic shielding does not account for the entry of fluid.
U.S. Pat. No. 4,962,826 to House discloses a damping treatment for bodies where the temperature may rise above 150.degree. C. which consists of a number of stand-off cantilever, sandwich type dampers, consisting of a layer of viso-elastic material sandwiched between two rigid metal plates. These plates are attached to a support that can be attached to the body. The support is thermally isolated from the body and is positioned at a position having a high amplitude of the radiating frequency that is to be reduced.
U.S. Pat. No. 5,253,680 to Matsumoto discloses a duplex metal pipe for damping wherein an inner pipe is inserted into an outer pipe with a clearance of 10 mm to 150 mm provided between surface of the outer pipe and the outer surface of the inner pipe. The outer pipe and inner pipe are formed of steel pipe. It is disclosed that within the specific clearance range, the effect of heat changes or damping can be overcome. However, Matsomoto does not account for expansion or bends in the pipe or allow environmental fluid to be incorporated in the area between the pipes.
Accordingly, the prior art does not provide for isolating the noise from the high-pressure steam traveling down the steam supply pipe from the fluid surrounding it to allow meaningful noise measurements of a vehicle under test.